1. Field of the Invention
This invention relates to an apparatus and a method for testing the operation of solenoid valves. More particularly, it pertains to a method and an apparatus for testing solenoid valves in a safety system of a process plant.
2. Description of the Prior Art
Modern process plants contain innumerable operating components. These components are tied together to form systems controlled by instrumentation and control systems containing sensors and controllers. The instrumentation and control systems on such plants not only serve to control the functions of the various components in order to achieve the desired process conditions, but they also provide the facility to safely modify or discontinue the operation of all or a portion of the plant's systems in order to avoid an unsafe situation or condition.
Safety systems require routine testing in order to verify that they continue to properly perform the functions for which they were intended. From an operational and economic point of view, they also should not modify or discontinue the operation of the plant system unnecessarily. One of the means by which such safety systems function is by the securing or diverting of the supply of a certain process fluid or the supply of motive power to a plant system or component of a plant system.
One of the means by which these safety functions can be accomplished is through the use of pneumatically operated valves. Such valves are operated by pneumatic actuators connected through solenoid operated pilot valves to the pneumatic control source.
In operation, the pneumatic actuators of such safety system valves are isolated from the pneumatic control source and pressure in the operator is vented off when the solenoid on the pilot valve is repositioned (e.g. de-energized). The safety system valve then changes position and the plant system is placed in the configuration designated for safety.
In some cases, individual input bypasses to the control system could not be exercised in order to test the operation of the pilot valve without actually tripping the system during testing.
Thus, there exists a need for a testing method and an apparatus to test the operation of solenoids in solenoid operated pilot valves for safety systems that does not negate the effectiveness of the safety system during the test phase and further does not require the plant system to be shut down during testing such that testing can be performed more frequently.